I tend to shudder when I hear customers say they’ve had walls re-plastered and painted them using a cheap contract paint as a basecoat. Simply because anything painted over this, even durable paints, will only be as durable or as sound as what’s underneath. If the basecoat rubs off then the rest of the paint layers will too.
Paint is only as good as the ingredients used to make it and if it’s cheap there’s a reason.
If you think of it like cooking, paint making is blending ingredients at room temperature. We’re dispersing powders into liquids. The final quality depends entirely on:
The quality of the raw materials (ingredients)
The amounts you add of each one
The care you take over making it
So what makes paint “good” from a user’s perspective?
Excellent coverage so you’re applying two coats at the most rather than three or four.
Ease of application so it goes where you want it to without drips or runs.
Excellent durability to withstands wear and tear and you can wash it down without having to worry about repainting.
The raw materials used in water based paints are typically:
Titanium Dioxide – white pigment, used in paints, plastics, paper, toothpaste and even sunscreen lotions. Used for opacity and “whiteness”. The more you add the better the coverage and the further the paint goes. Cost around £3000/tonne currently.
Fillers – chalk (calcium carbonate), calcined or heat-treated chalk (whiter), talc or Dolomite clays (harder, flatter particles which add durability). These add body by increasing the viscosity. Cost £200 - £500/tonne. Cheaper paints will contain a much higher percentage of these than Titanium Dioxide to reduce the cost.
Binders or Resins – emulsion polymers which hold the paint together. Costs can vary from less than £1000 /tonne to £1500 +/ tonne depending on the type and quality. If you buy cheap paint, it will have the minimal amount in to hold it all together and won’t have any durability or scrub resistance to speak of.
Rheology Control Additives – there’s numerous choices ranging from cellulosic thickeners to associative or polymeric thickeners. These prevent the paint from separating, give it its viscosity and allow a smooth and even application whilst minimising roller splatter, drips and runs.
Additives – including Dispersantsto separate the powder particles in the water phase and prevent them re-agglomerating and then settling at the bottom of the container. Defoamersto prevent foam forming during mixing (defoaming) or stop air bubbles getting trapped in the paint film as it’s applied (anti-foams). Biocides or in can preservatives which are essential to stop the liquid paint being degraded by airborne bacteria. Paint will go off like milk or yoghurt but should last for at least a year in sealed containers. As they kill “bugs” biocides are active chemicals and depending on the amounts added, you may see them listed n the back of paint tins warning about possible skin sensitization.
Last but not least – Pigments. Unlike dyes, these are insoluble in water and can be added as dry powders or more commonly as pigment dispersions where the dry powders are pre-mixed into a liquid. Due to the incredible choice of paints colours available nowadays, most paint are tinted to order using recipes of different coloured pigment dispersions.
In conclusion, paint is like a lot of things – you get what you pay for!
Paint that costs around £1 per litre will contain an awful lot of water and Calcium Carbonate (chalk) and other inexpensive fillers. You’ll get very little Titanium Dioxide and very little binder, the minimal amount to hold it together.
As a result, you’ll end up with a chalky or powdery finish on the walls and anything that goes over this and it could be a really expensive paint, won’t stick properly to a powdery surface. The whole lot will scrub off.
So if you’re thinking “it’s only a basecoat, it doesn’t matter”, it really is a false economy.